From the Ritual of the Blight quest introduced in Shattered Lines.
Located at 84.1N 44.1E on the south beach of the west side of Aerlinthe Island. Either run around the harbor, around the island perimeter beach, or use Coral Tunnels to get across the harbor.
The pyramid's light is strengthening, but there will be a long way to go before it is restored. It has not yet reached half strength.
Search for Blighted Pyreal Golems on the north side of Aerlinthe Island, they drop Blighted Mana Crystals. Give their trophies to the Node, see A Field Guide to Tainted Nodes for details.